The present invention relates generally to radiators, and more particularly, to the use of a centered longitudinal shunt slot disposed in a broadwall of a rectangular waveguide that is fed by an offset ridge resonant iris.
An advanced seeker under development by the assignee of the present invention requires a common aperture dual polarized antenna. There are several ways to provide a dual polarized antenna having a common aperture. To provide a large aperture, a dipole array and slot array combination is very attractive. For this combination, centered longitudinal shunt slots must be used because an offset longitudinal shunt slot excites not only a desired lowest parallel plate mode but also undesirable higher order modes in the parallel plate region created by the dipole array. The centered longitudinal shunt slot excites only the desired lowest mode (TEM).
However, a centered longitudinal broadwall slot in a rectangular waveguide does not radiate because the centered longitudinal slot does not disturb the current flow of the TE10 mode. The prior art used an L-shaped offset resonant iris to excite the centered longitudinal slot.
Centered longitudinal broadwall slots fed by L-shaped resonant irises have heretofore been used to produce a linear antenna array. This antenna array is disclosed in a paper by R. Tang, entitled "A slot with variable coupling and its application to a linear array:, IRE Trans. AP-8, p. 97, 1960. This linear antenna array has a relatively inefficient layout, exhibits an undesirable phase change in terms of offset variation, has a somewhat unstable conductance range, and is relatively difficult to machine and dip braze.
Accordingly, it is an objective of the present invention to provide for the use of a centered longitudinal shunt slot disposed in a broadwall of a rectangular waveguide that is fed by an offset ridge resonant iris, and which is particularly well adapted for use in a common aperture dual polarized antenna.